In article after article, academics, policy analysts, and journalists have told a similar story: climate change, by melting Arctic ice, is unlocking resources that could soon trigger war in the far north. They argue that the race to extract the vast reservoirs of oil and natural gas that lie under the vanishing ice – up to a quarter of the world’s undiscovered fossil fuel reserves, by some estimates – will likely provoke hostilities between Russia, the United States, and other nations with claims to the bonanza. The overall failure of early drilling efforts in the Arctic, it seems, is of little consequence.

These claims add a new twist to a vast and growing body of scholarship that links climate change to conflict. Academics working in this area often begin their work by showing that past climate changes reduced – rather than increased – the regional availability of some crucial resource, such as water, or grain, or fish spawning grounds. They then use diverse methods to trace the destabilizing social and political consequences of these resource shortages. Environmental historians, for example, have argued that falling temperatures and changing precipitation patterns in the seventeenth century led to poor grain harvests and famines that provoked rebellions in diverse societies the world over. More controversially, scholars in many disciplines have linked human-caused global warming to droughts that encouraged migration and ultimately conflict in twentieth-century sub-Saharan Africa. Far less attention has been directed at the ways in which more abundant resources might incite violence either within or between states.

In fact, those who make claims about the inevitably more violent nature of the future Arctic have rarely thought to consider the history of climate change and conflict in the far north. Yet violence in the Arctic has long coincided with volcanic eruptions and fluctuations in solar activity that altered regional temperatures and in turn the availability of crucial resources. In the early seventeenth century, for example, the Arctic cooled sharply and then warmed slightly just as Europeans discovered, hunted, and fought over bowhead whales off Spitsbergen, the largest island of the Svalbard archipelago. Oil, bones, and baleen from bowheads became crucial resources for the economies of England and the Dutch Republic.

​Diverse manifestations of climate change in the Arctic and Europe influenced how easy bowhead whales were to hunt, the profits that could be fetched by their oil, the proximity of whalers to one another, and the ability of whalers to reach the far north. Skirmishes within and between whaling companies operating from rival European nations reveal that climate change can affect both the causes and the conduct of conflict in diverse ways, even in environments it transforms on a vast scale. There is nothing inevitable or simple about the ways in which climate change influences human decisions and actions.

Svalbard, roughly halfway between Norway and the North Pole. Spitsbergen is the big island on the left.

​This history would be hard to investigate without new climate reconstructions compiled by scholars in many different disciplines, using many different sources. In 2014, researchers drew from natural and textual sources to create a sweeping new reconstruction of average Arctic air surface temperatures over the past 2,000 years. It confirms that the Arctic was overall very cold in the seventeenth century, but also that it warmed slightly towards the middle and end of the century. Temperatures in the Arctic therefore roughly mirrored those elsewhere in the Northern Hemisphere during the chilliest century of the “Little Ice Age,” a cooler climatic regime that endured for roughly six centuries. The extent and distribution of sea ice in the Arctic – the most important environmental condition that whalers coped with – would have responded to even subtle changes in average annual temperatures.

Yet these very big trends do not tell us exactly how climate change transformed environments around Svalbard. Local temperature trends do not always precisely mirror regional or global developments, and anyway the distribution and extent of Arctic sea ice registers more than just the warmth or chilliness of the lower atmosphere. Ice core and model simulation data both suggest that air surface temperatures around Svalbard were quite cool in the early seventeenth century and somewhat warmer in the middle of the century, at least in summer. Lakebed sediments, by contrast, suggest that glaciers across Svalbard actually retreated beginning in around 1600 owing to changes in precipitation, not temperature, which may have reduced the local frequency of storms that can break up sea ice. Moreover, sea surface temperatures – which also influence sea ice – were quite warm off the west coast of Spitsbergen, the largest island of the Svalbard archipelago, for much of the seventeenth century, although they were very cold off the northern coast.

A 2014 revision (red) of a PAGES 2K reconstruction (black) of annual average temperatures across the Arctic, compiled using diverse scientific and historical sources.

​Overall, it seems safe to conclude that, in the summer, temperatures around Svalbard roughly mirrored those of the broader Arctic in the seventeenth century. Warmer currents may have brought more nutrients to the region and probably reduced the extent of local sea ice, although a reduction in storm frequency would have preserved the ice that was there. In any case, most Arctic sea ice melts in the summer before reaching its minimum annual extent in the fall, which means that summer weather and currents had the greatest impact on the extent of ice in the Arctic north of Europe. Because sea ice retreated from Svalbard in the summer, it was also the crucial season for whaling.

If the local consequences of global climate changes can be counterintuitive – that warming current off Spitsbergen, for example – so too can human responses. One might assume that climatic cooling would have dissuaded explorers, fishers, and whalers from entering the Arctic. Instead, European sailors found and then started exploiting the environments on and around Svalbard in the late sixteenth and early seventeenth centuries, just as volcanic eruptions led to arguably the coldest point of the Little Ice Age in the Northern Hemisphere. In previous work, I have shown that climate changes in this period interacted with local environments to leave just enough sea ice in the Arctic north of Europe to redirect expeditions in search of an elusive “Northern Passage” to Asia. Dutch and English sailors struggling to find a way through the ice ended up discovering Spitsbergen and the many bowhead whales off its western coast. Bowheads are relatively docile, float on the surface when killed, and have very thick blubber that can be turned into oil. Beginning in 1611, they started attracting Dutch, English, and Basque whalers.

Other scholars have argued that cooling in the early seventeenth century led bowhead whales to congregate along more extensive sea ice near Spitsbergen, which made them easier to hunt for whalers. By contrast, whales dispersed as sea ice retreated in the warmer middle of the seventeenth century, which made them harder to hunt. There does seem to be a statistically significant correlation between ice core reconstructions and model simulations of summer temperatures around Spitsbergen on the one hand, and the annual whale catch on the other. Iñupiat whalers consulted by our own Bathsheba Demuth, however, report that bowheads in the Berring Sea are not social enough to gather in huge groups. Perhaps bowhead culture was different in the Atlantic corner of the Arctic when whale populations were much higher than they are today.

The apparent correlation between surface air temperatures and the whale catch around Spitsbergen provides our first point of entry into relationships between climate change and conflict in the far north. From the first years of whaling around Spitsbergen, two companies – the Dutch Northern Company, and the English Muscovy Company – emerged as the leading players in the Arctic whaling industry. The governments of England and the Dutch Republic had granted these companies monopolies on whaling operations, but they were resented by merchants and mariners who preferred to operate independently. After around 1625, as bowhead whales dispersed amid warming temperatures, competition between Dutch whalers devolved into piracy. Many conflicts involved whalers who sailed either for the Northern Company or for themselves, although even some Company whalers hid the best hunting grounds from one another. In these circumstances, the governing body of the Dutch Republic rescinded the monopoly of the Northern Company in 1642.

From the beginning, competition between English whalers assumed an even more brutal character. The Muscovy Company took an uncompromising stance towards English interlopers, who responded in turn. In 1626, for example, whalers aboard independently-owned vessels destroyed the Company’s station at Horn Sound, Spitsbergen, after they had been harassed by Company ships. Not surprisingly, petitions submitted to the English Standing Council for Trade in 1652 reveal that small groups of English merchants also sought to overturn the monopoly of the Muscovy Company. Individual merchants insisted that the Company could not adequately “fish” the territories over which it held a monopoly. The Company responded that whalers in the employ of those merchants had interfered with the activities of its sailors and stolen whales they had killed.

Warming temperatures that reduced the extent of pack ice and encouraged whales to disperse may well have encouraged competition and conflict between whalers belonging to the same nationality. Bizarrely, the whaling industry also responded to fluctuations in the supply of rape, linseed and hemp oils, which were less smelly substitutes to whale oil for fueling lamps or manufacturing soap, leather, or wax. Temperature and precipitation extremes that reduced the supply of vegetable oils naturally also increased the price of whale oils in the Dutch and English economies, and thereby the profitability of whaling. In the context of the Little Ice Age, the 1630s in particular were relatively warm across the Northern Hemisphere. The trusty Allen-Unger commodity database tells us that the price of linseed oil in Augsburg, for example, dropped sharply as average annual temperatures increased. Even the price of lamp oil – which would have also registered the price of whale oil – fell modestly in the same period. Could whalers in the 1630s and 1640s have vied with monopolistic companies just climate change both reduced the supply of their resource and increased its profitability?

A possible depiction of Smeerenburg (although another version of the same painting has Danish flags, and the mountain in the background resembles the volcano on Jan Mayen Island).

​We can sketch these relationships by mixing and matching different statistics from natural and textual archives. Detailed qualitative accounts written by whalers, however, reveal that climate influenced conflict in more complicated ways during the first decade of the Svalbard whaling industry. In that decade, whalers from several European nations – most importantly England and the Dutch Republic – employed experienced Basque whalers to kill bowhead whales, strip their blubber, and boil the blubber on the coast. Whalers would deploy boats from a mothership to kill small groups of whales. They would then establish temporary settlements on the coast to turn the blubber into oil that could be loaded into barrels and returned to the ship.

These techniques forced whalers from different nations to rove along the coast of Spitsbergen, which made it likely that they would encounter one another. Initially, the Muscovy Company falsely claimed that English explorers had found Spitsbergen, which meant that it alone had the right to hunt for whales off the island. The Dutch – who had actually discovered the island – insisted that whalers from all European nations should be allowed to fish off its coast. In 1613, a Dutch expedition under Willem van Muyden, the legendary “First Whaleman” of the Republic, reached Spitsbergen in late May and found the coast blocked by ice. After only two weeks, the retreating ice let his whalers enter a bay roughly halfway down the island, but a better-armed English fleet quickly spotted them. In subsequent weeks, the English harassed the Dutch whalers and stole much of their equipment and whale commodities. Yet the Dutch returned with naval escorts in 1614. After the English seized a Dutch ship in 1617, the Dutch arrived with overwhelming force in 1618 and killed several English whalers.

Grønfjorden, Spitsbergen, where the hostilities of 1613 began.

The worst skirmishes between Dutch and English whalers raged in years that were relatively warm across the Arctic and probably around Svalbard, despite the generally cooler climate of the early seventeenth century. In cold years, sea ice could have kept whalers working for different companies from lingering on the coast, where tensions simmered and eventually erupted into bloodshed. In any case, the Muscovy Company and the Northern Company eventually agreed to occupy different parts of Spitsbergen. The Dutch would claim the northwestern tip, where they established the major, fortified settlement of Smeerenburg: “blubber town.” The English, meanwhile, took the rest. The Dutch eventually benefited from being closer to the edge of the summer pack ice, where there were more whales to hunt.

Hostilities between the English and the Dutch in the volatile first decades of the Svalbard whaling industry convinced the Northern Company to keep a skeleton crew at Smeerenburg and nearby Jan Mayen island during the winter. If they could survive, they would keep Company infrastructure safe from springtime raids and provide valuable information about the region’s winter weather. In 1633/34, two groups of Dutch whalers overwintered at Smeerenburg and Jan Mayen. Regional summer temperatures may have been warming at the time, but winter temperatures across the Arctic were cooling, and 1633/34 was particularly cold. The Smeerenburg group survived the frigid temperatures and killed enough caribou and Arctic foxes to hold off scurvy. The Jan Mayen whalers endured until the spring, but they could not catch enough game to survive the ravages of scurvy. In 1634/35, the Northern Company tried again. This time, both groups died from scurvy, and the Smeerenburg whalers did not even make it to winter. Violent competition between whaling companies – plausibly influenced by warming summers – exposed whalers to a quirk in the climatic trends of the Little Ice Age in the Arctic: the big difference between summer and winter temperatures, relative to long-term averages.

Climate change also influenced hostilities between whalers by altering how easily they could reach the “battlefield” around Spitsbergen. In 1615, a year of typical chilliness during the Little Ice Age, the author of a Dutch whaling logbook reported that sea ice on June 7th blocked the crew’s progress towards Svalbard. The crew spotted a bowhead whale three days later, but ice kept them from pursuing. That evening, a storm rose just as they found themselves surrounded by sea ice. They tried to anchor themselves to an iceberg, but it shattered and would have destroyed their ship “had God not saved us.” The few surviving logbooks written by Dutch whalers also record trouble with ice in the warmer 1630s, yet it surely would have been harder to reach Svalbard and compete with English whalers in the first decade of the Arctic whaling industry.

Dutch whaling logbook written on a voyage to Spitsbergen in 1615.

​Beginning in 1652, the Dutch Republic and England also embarked on hostilities in the North Sea region that would endure, with interruptions, until the Dutch invasion that launched the Glorious Revolution of 1688. During the three Anglo-Dutch Wars that raged in these decades, English and Dutch ordinance kept whalers from sailing to the Arctic or constructing new ships and equipment for the whaling industry. Sailors who might have served aboard whaling ships were urgently needed to crew the warships of the English and Dutch fleets. Many whalers also served as privateers, raiding merchant ships and convoys and then surrendering a share of the profits to their governments. Any whalers who set sail for the Arctic risked losing everything if discovered.

As I have written elsewhere, a cooling climate in the second half of the seventeenth century profoundly influenced naval hostilities between the English and Dutch fleets. By altering the frequency of easterly and westerly winds in the North Sea, it helped the English claim victory in the First Anglo-Dutch War but aided the Dutch in the Second and Third Anglo-Dutch Wars, as well as the Glorious Revolution. It probably shortened the First Anglo-Dutch War (1652-54) but lengthened the third war (1672-74). That, in turn, would mean that the manifestations of global climate change in the North Sea affected the opportunities for whalers to engage in hostilities in the Arctic.

Ordinance forbidding whaling issued by the States-General, the Dutch ruling body, in 1673.

After 1650, the character of hostilities between Arctic whalers changed dramatically. Cooling summer temperatures brought thick ice into the harbors of Spitsbergen, while the depletion of the bowhead whale population may have worsened the prospects of whaling near land. Whalers had to hunt further and further from the shore, and started processing their whales at sea. They abandoned settlements along the coast of Spitsbergen, which soon fell into ruin. Violence between whalers now took place exclusively at sea. The evidence is spotty, but privateers seem to have hunted whalers in the final decades of the seventeenth century. In 1692, Henry Greenhill, commissioner of the English navy at Plymouth, reported that two “Greenland Prizes” – whaling vessels captured off Spitsbergen – had been brought into harbor. Since England had allied with the Dutch Republic against France, these ships were probably French in origin.

The history of climate change, whaling, and violence in and around Svalbard during the seventeenth century is above all complicated, filled with surprising twists and turns. Climate change may have occasionally provoked violence, but it probably did so by reducing, rather than increasing, the accessibility of bowhead whales to whalers. More importantly and more certainly, it altered the character of confrontations between whalers in the far north. Moreover, its manifestations thousands of kilometers from the Arctic ended up having important consequences for hostilities in and around Svalbard.

These intricate relationships in the distant past should give us pause as we contemplate the warmer future in the Arctic. Global warming may indeed set the stage for war in the far north, but we have no way of knowing for sure. It is equally likely that climate change will provoke human responses that are hard to guess at present. In this case, we cannot use the past to predict the future, but we can draw on it to ask more insightful questions in the present.

In the year 1001 CE, Leif Erikson made landfall in Greenland, and traded with people who “in their purchases preferred red cloth; in exchange they had furs to give.” The Vikings called these people Skraelings. Present-day archeologists and historians call them the Thule. At its height, Thule civilization spread from its origins along the Bering Strait across the Canadian Arctic and into to Greenland. The ancestors of today’s Inuit and Inupiat, the Thule accomplished what Erikson and subsequent generations of Europeans never managed: living in the high Arctic without supplies of food, technology, and fuel from more temperate climates.

The Thule left archeological evidence of a technologically sophisticated, vigorous people. They invented the umiak, an open walrus-hide boat so large that it was sometimes equipped with a sail. These boats, when used alongside small, nimble kayaks, made the Thule formidable marine-mammal hunters. On land, they harnessed dogs to sleds and built homes half-underground, insulated by earth and beamed with whale bones.

People did inhabit the high North American Arctic before the Thule. Their immediate predecessors, called the Dorset by archeologists, were expert carvers, and there are signs of other cultures that date back at least five thousand years. But the Thule appear to have been a particularly robust society, one that inhabited thousands of challenging Arctic miles. Eventually, they even traded with Europeans for metal tools, sending walrus ivory as far abroad as Venice.

In the twentieth century, many archeologists linked the success of the Thule to the climate. In this view, rapid Thule expansion coincided with the Medieval Warm Period in the years between 1000 and 1300. The Thule were expert whalers, especially of bowhead whales. This slow species makes for good prey. Their 100-ton bodies can be fifty percent fat by volume, giving people ample calories to eat and burn through long winters. With the slight increase in temperature during the Medieval Warm Period, the theory went, the range of the bowhead whale expanded across newly ice-free waters. Atlantic and Pacific bowhead populations eventually met in the Arctic Ocean north of Canada, offering an uninterrupted banquet of blubber to hunters.

​The Thule, in this view, were simply whale hunters who followed the migration of their prey in a warming climate. Environmental conditions, not a sophisticated culture, was the key explanation for their success. Emphasizing climate as the cause of migration and social success reduced the achievements of the Thule, essentially, to those of their prey.

However, twenty-first century evidence is changing this account of Thule migration. In 2000, Robert McGhee questioned the validity of the radiocarbon dates that helped establish Thule expansion as an eleventh-century phenomenon. He proposed the 1200s as the earliest date of migration. Then, genetic tests by marine biologists showed that Atlantic and Pacific bowhead whales did not mix their populations during the Medieval Warm Period, meaning that there was a substantial gap in whaling possibilities on the Arctic coast.

Something more complicated than just following the blubber drove the Thule eastward. McGhee speculated that communities moved for iron, which is short supply in the Arctic. Thule hunters learned from the Dorset people of a deposit left by the Cape York meteorite. They colonized huge territories to secure their access to this precious resource from outer space. Other specialists theorized that population pressure, overhunting, or warfare led the Thule to migrate east.

The ongoing work of Canadian archeologists T. Max Friesen and Charles D. Arnold seems to confirm that we must look beyond simple climatic explanations for the Thule expansion. Working on Beaufort Sea and Amundsen Gulf sites, the pair established that there was no definitive Thule occupation in this part of the western Arctic prior to the thirteenth century. Because any Thule migrants would have had to pass through these points as they moved east, their research indicates that the Thule civilization was only beginning its continental spread around the year 1200, well into the period of warming. The climate may have helped the Thule quickly spread toward Greenland, but the onset of the Medieval Warm Period did not automatically draw people eastward.

Moreover, the work of other archeologists on the Melville Peninsula, along Baffin Bay, indicates that the Mediaeval Warm Period was not always so warm. Some areas of the Arctic saw slight temperature increases, but in general the millennium was cooler than those past. In places, the effects of the so-called Little Ice Age began a century or two before they were evident across the globe, meaning the Thule adapted not to a warmer Arctic, but a colder one. This cooling was more apparent in the west, where the team found fewer Thule sites but also more stability, both in the climate and the record of human occupation. To the east of the Melville Peninsula, where temperatures did warm, the climate was also more variable – adding a new set of complexities to social and economic life. The move into the central Arctic, therefore, reflected forces other than climate.

Beginning in the fifteenth century, Thule culture fragmented, specialized, and emerged eventually as distinct contemporary Inuit and Inupiat groups. The Little Ice Age is often the reason given for the disintegration of Thule civilization in the fifteenth century. Yet, the work by Finkelstein, Ross, and Adams indicates that, while the Thule abandoned some sites due to cooling trends, this did not hold in all cases. Other causes, including increased contact with Europeans and their infectious diseases, might have had more to do with the disintegration in some locations.

Overall, the new vision of the Thule prominence in the Arctic makes their rise shorter, but even more impressive. And if the Thule began their migration only in 1200, it seems unlikely they spread east simply to find iron. This would have required only smaller-scale movements to precise locations. Instead, the Thule developed a thriving, intricate network of settlements across the Arctic. For Friesen and Arnold, this is evidence that the Thule expanded in order to recreate the ideological and economic lives that they had enjoyed in their origins along the Bering Strait. And in just a century they did, not only by inhabiting land from the Bering Strait to Greenland, but through explorations to the northern edges of the continent.

All of this also helps us reinterpret a well-known tale from the Viking exploration of the Arctic. When Leif Erikson’s sister Freydis frightened off a band of Skraelingar in the early eleventh century by striking “her breast with the naked sword” of a fallen Viking, she was likely not fighting the Thule, as scholars have assumed. Perhaps it was the Dorset people that “were frightened, and rushed off in their boats.” The Thule, at least, were likely still a century away from the eastern Canadian coastline. They were not easily daunted either by a shifting climate or by Viking weapons.

McGhee, Robert. “Radio Carbon Dating and the Timing of the Thule Migration,” in Appelit, M. Berglund, J, and Gullov, H.C. eds. Identities and Cultural Contacts in The Arctic: Proceedings from a Conference at the Danish National Museum. Copenhagen (2000): 181-191.

Dyke, Arthur S., James Hooper, and James M. Savelle. “A History of Sea Ice in the Canadian Arctic Archipelago based on Postglacial Remains of the Bowhead Whale (Balaena mysticetus)”, Arctic 49 (1996): 235-255.

Park, Robert W. “The Dorset-Thule Succession Revisited,” in Appelit, M. Berglund, J, and Gullov, H.C. eds. Identities and Cultural Contacts in the Arctic: Proceedings from a Conference at the Danish National Museum. Copenhagen (2000): 192-205.

It's Maunder Minimum Month at HistoricalClimatology.com. This is our first of two feature articles on the Maunder Minimum. The second, by Gabriel Henderson of Aarhus University, will examine how astronomer John Eddy developed and defended the concept.

​Although it may seem like the sun is one of the few constants in Earth’s climate system, it is not. Our star undergoes both an 11-year cycle of waning and waxing activity, and a much longer seesaw in which “grand solar minima” give way to “grand solar maxima.” During the minima, which set in approximately once per century, solar radiation declines, sunspots vanish, and solar flares are rare. During the maxima, by contrast, the sun crackles with energy, and sunspots riddle its surface.

The most famous grand solar minimum of all is undoubtedly the Maunder Minimum, which endured from approximately 1645 until 1720. It was named after Edward Maunder, a nineteenth-century astronomer who painstakingly reconstructed European sunspot observations. The Maunder Minimum has become synonymous with the Little Ice Age, a period of climatic cooling that, according to some definitions, endured from around 1300 to 1850, but reached its chilliest point in the seventeenth century.

​During the Maunder Minimum, temperatures across the Northern Hemisphere declined, relative to twentieth-century averages, by about one degree Celsius. That may not sound like much – especially in a year that is, globally, still more than one degree Celsius hotter than those same averages – but consider: seventeenth-century cooling was sufficient to contribute to a global crisis that destabilized one society after another. As growing seasons shortened, food shortages spread, economies unraveled, and rebellions and revolutions were quick to follow. Cooling was not always the primary cause for contemporary disasters, but it often played an important role in exacerbating them.

Life on the ice in Amsterdam, during a typically frigid winter in the Maunder Minimum. Source: Jan Abrahamsz. Beerstraten, "Het Paalhuis en de Nieuwe Brug te Amsterdam in de Winter," 1640-1666.

Many people – scholars and journalists included – have therefore assumed that any fall in solar activity must lead to chillier temperatures. When solar modelling recently predicted that a grand solar minimum would set in soon, some took it as evidence of an impending reversal of global warming. I even received an email from a heating appliance company that encouraged me to hawk their products on this website, so our readers could prepare for the cooler climate to come! Of course, the warming influence of anthropogenic greenhouse gases will overwhelm any cooling brought about by declining solar activity.

In fact, scientists still dispute the extent to which grand solar minima or maxima actually triggered past climate changes. What seems certain is that especially warm and cool periods in the past overlapped with more than just variations in solar activity. Granted, many of the coldest decades of the Little Ice Age coincided with periods of reduced solar activity: the Spörer Minimum, from around 1450 to 1530; the Maunder Minimum, from 1645 to 1720; and the Dalton Minimum, from 1790 to 1820. However, one of the chilliest periods of all – the Grindelwald Fluctuation, from 1560 to 1630 – actually unfolded during a modest rise in solar activity. Volcanic eruptions, it seems, also played an important role in bringing about cooler decades, as did the natural internal variability of the climate system. Both the absence of eruptions and a grand solar maximum likely set the stage for the Medieval Warm Period, which is now more commonly called the Medieval Climate Anomaly.

This gets to the heart of what we actually mean when we use a term like “Maunder Minimum” to refer to a period in Earth’s climate history. Are we talking about a period of low solar activity? Or are we referring to an especially cold climatic regime? Or are we talking about chilly temperatures and the changes in atmospheric circulation that cooling set in motion? In other words: what do we really mean when we say that the Maunder Minimum endured from 1645 to 1720? How does our choice of dates affect our understanding of relationships between climate change and human history in this period?

​To find an answer to these questions, we can start by considering the North Sea region. This area has yielded some of the best documentary sources for climate reconstructions. They allow environmental historians like me to dig into exactly the kinds of weather that grew more common with the onset of the Maunder Minimum. In Dutch documentary evidence, for example, we see a noticeable cooling trend in average seasonal temperatures that begins around 1645. On the surface of things, it seems like declining solar activity and climate change are very strongly correlated.

And yet, other weather patterns seem to change later, one or two decades after the onset of regional cooling. Weather variability from year to year, for example, becomes much more pronounced after around 1660, and that erraticism is often associated with the Maunder Minimum. Severe storms were more frequent only by the 1650s or perhaps the 1660s, and again, such storms are also linked to the Maunder Minimum climate. In the autumn, winter, and spring, easterly winds – a consequence, perhaps, of a switch in the setting of the North Atlantic Oscillation – increased at the expense of westerly winds in the 1660s, not twenty years earlier.

All of these weather conditions mattered profoundly for the inhabitants of England and the Dutch Republic: maritime societies that depended on waterborne transportation. Rising weather variability made it harder for farmers to adapt to changing climates, but often made it more profitable for Dutch merchants to trade grain. More frequent storms sank all manner of vessels but sometimes quickened journeys, too. Easterly winds gave advantages to Dutch fleets sailing into battle from the Dutch coast, but westerly winds benefitted English armadas. If we define the Maunder Minimum as a climatic regime, not (just) a period of reduced sunspots, and if we care about its human consequences, what should we conclude? Did the Maunder Minimum reach the North Sea region in 1645, or 1660?

​These problems grow deeper when we turn to the rest of the world. Across much of North America, temperature fluctuations in the seventeenth century did not closely mirror those in Europe. There was considerable diversity from one North American region to another. Tree ring data suggests that northern Canada appears to have experienced the cooling of the Maunder Minimum. Western North America also seems to have been relatively chilly in the seventeenth century, although there chillier temperatures probably did not set in during the 1640s.

By contrast, cooling was moderate or even non-existent across the northeastern United States. Chesapeake Bay, for instance, was warm for most of the seventeenth century, and only cooled in the eighteenth century. Glaciers advanced in the Canadian Rockies not in the seventeenth century, but rather during the early eighteenth century. Their expansion was likely caused by an increase in regional precipitation, not a decrease in average temperatures.

Still, the seventeenth century was overall chillier in North America than the preceding or subsequent centuries, and landmark cold seasons affected both shores of the Atlantic. The consequences of such frigid weather could be devastating. The first settlers to Jamestown, Virginia had the misfortune of arriving during some of the chilliest and driest weather of the Little Ice Age in that region. Crop failures contributed to the dreadful mortality rates endured by the colonists, and to the brief abandonment of their settlement in 1610.

An early seventeenth-century map of New France. Just look at all those trees! Source: Samuel de Champlain, "Map of New France," 1612.

Moreover, many parts of North America do seem to have warmed in the wake of the Maunder Minimum, in the eighteenth century. This too could have profound consequences. In the seventeenth century, settlers to New France had been surprised to discover that their new colony was far colder than Europe at similar latitudes. They concluded that its heavy forest cover was to blame, and with good reason: forests do create cooler, cloudier microclimates. Just as the deforestation of New France started transforming, on a huge scale, the landscape of present-day Quebec, the Maunder Minimum ended. Settlers in New France concluded that they had civilized the climate of their colony, and they used this as part of their attempts to justify their dispossession of indigenous communities.

Despite eighteenth-century warming in parts of North America, the dates we assign to the Maunder Minimum do look increasingly problematic when we look beyond Europe. If we turn to China, we encounter a similar story. Much of China was actually bitterly cold in the 1630s and early 1640s, before the onset of the Maunder Minimum elsewhere. This, too, had important consequences for Chinese history. Cold weather and precipitation extremes ruined crops on a vast scale, contributing to crushing famines that caused particular distress in overpopulated regions. The ruling Ming Dynasty seemed to have lost the “mandate of heaven,” the divine sanction that, according to Confucian doctrine, kept the weather in check. Deeply corrupt, riven by factional politics, undermined by an obsolete examination system for aspiring bureaucrats, and scornful of martial culture, the regime could adequately address neither widespread starvation, nor the banditry it encouraged.

Climatic cooling caused even more severe deprivations in neighboring, militaristic Manchuria. There, the solution was clear: to invade China and plunder its wealth. The first Manchurian raid broke through the Great Wall in 1629, a warm year in other parts of the Northern Hemisphere. Ultimately, the Manchus capitalized on the struggle between Ming and bandit armies by seizing China and founding the Qing (or "Pure") Dynasty in 1644.

China under the Ming Dynasty was arguably the most powerful empire of its time. Even as it unravelled in the early seventeenth century, its cultural achievements were impressive, as this painting of fog makes clear. Source: Anonymous, "Peach Festival of the Queen Mother of the West," early 17th century.

This entire history of cooling and crisis predates the accepted starting date of the Maunder Minimum. Yet, the fall of the Ming Dynasty unfolded in one relatively small part of present-day China. Average temperatures in that region reached their lowest point in the 1640s. By contrast, average temperatures in the Northeast warmed by the middle of the seventeenth century. Average temperatures in the Northwest also warmed slightly during the mid-seventeenth century, and then cooled during the late Maunder Minimum.

​Smoothed graphs that show fluctuations in average temperature across centuries or millennia give the impression that dating decade-scale warm or cold climatic regimes is an easy matter. Actually, attempts to precisely date the beginning and end of just about any recent climatic regime are sure to set off controversy. This is not only because global climate changes have different manifestations from region to region, but also because climate changes, as we have seen, involve much more than shifts in average annual temperature. Did the Maunder Minimum reach northern Europe, for instance, when average annual temperatures declined, when storminess increased, when annual precipitation rose or fell, or when weather became less predictable?

Historians such as Wolfgang Behringer have argued that, when dating climatic regimes, we should also consider the “subjective factor” of human reactions to weather. For historians, it makes little sense to date historical periods according to wholly natural developments that had little impact on human beings. Maybe historians of the Maunder Minimum should consider not when temperatures started declining, but rather when that decline was, for the first time, deep enough to trigger weather that profoundly altered human lives. When we consider climate changes in this way, we may be more inclined to subjectively date climatic regimes using extreme events, such as especially cold years, or particularly catastrophic storms. Dating climate changes with an eye to human consequences does take historians away from the statistical methods and conclusions pioneered by scientists, but it also draws them closer to the subjects of historical research.

In my work, I do my best to combine all of these definitions, and incorporate many of these complexities. I date climatic regimes by considering their cause – solar, volcanic, or perhaps human – and by working with statisticians who can tell me when a trend becomes significant. However, I also try to consider the many different kinds of weather associated with a climatic shift, and the consequences that extremes in such weather could have for human beings.

As you might expect, this is not always easy. I have long held that the Maunder Minimum, in the North Sea region, began around 1660. Increasingly, I find it easier to begin with the broadly accepted date of 1645, but distinguish between different phases of the Maunder Minimum. An earlier phase marked by cooling might have started in 1645, but a later phase marked by much more than cooling took hold around 1660.

These are messy issues that yield messy answers. Yet we must think deeply about these problems. Not only can such thinking affect how we make sense of the deep past, but it can also provide new perspectives on modern climate change. When did our current climate of anthropogenic warming really start? At what point did it start influencing human history, and where? What can that tell us about our future? These questions can yield insights on everything from the contribution of climate change to present-day conflicts, to the timing of our transition to a thoroughly unprecedented global climate, to the urgency of mitigating greenhouse gas emissions.

​Ask most people about climate change, and you will soon find that even the relatively informed make two big assumptions. First: the world’s climate was more or less stable until recently, and second: human actions started changing our climate with the advent of industrialization. If you have spent any time reading through this website, you will know that the first assumption is false. For millions of years, changes in Earth’s climate, driven by natural forces, have radically transformed the conditions for life on Earth. Admittedly, the most recent geological epoch – the Holocene – is defined, in part, by its relatively stable climate. Nevertheless, regional and even global climates have still changed quickly, and often dramatically, in ways that influenced societies long before the recent onset of global warming.

Take, for example, the sixteenth century. Relative to early twentieth-century averages, the decades between 1530 and 1560 were relatively mild in much of the northern hemisphere. Yet, after 1565, average annual temperatures in the northern hemisphere fell to at least one degree Celsius below their early twentieth-century norms. Despite substantial interannual variations, temperatures remained generally cool until the aftermath of a bitterly cold “year without summer,” in 1628. Since the expansion of the glacier near Grindelwald, a Swiss town, was among the clearest signs of a chillier climate, these decades are collectively called the “Grindelwald Fluctuation.” It was one of the coldest periods in a generally cool climatic regime that is today known as the “Little Ice Age.”

Length changes of four well-documented Alpine glaciers, based on historical sources.

​Volcanic eruptions undoubtedly caused some of the cooling. In 1595, the eruption of Nevado del Ruiz released sulphur aerosols into the atmosphere, scattering sunlight and thereby cooling the planet. Just five years later, Huaynaputina exploded in one of the most powerful volcanic explosions of the past 2,500 years. Major volcanic eruptions following in close proximity to one another can trigger long-term cooling by activating "positive feedbacks" in different parts of Earth’s climate system. In the Arctic, for example, volcanic dust veils lead to chillier temperatures, which can increase the extent of Arctic ice that, through its high albedo, reflects more sunlight into space than the water or land it replaces. That in turn leads to even cooler temperatures, more ice, and so on.

However, the onset of the Grindelwald Fluctuation preceded the eruption of Nevado del Ruiz by some thirty years. Clearly, volcanoes were not the only culprits for the colder climate. Some scientists believe that low solar activity also played a role. Yet, although the sun was less active during the Grindelwald Fluctuation than it is today, it will still more active than it was in most other decades of the Little Ice Age.

Solar minima and maxima over the past 2,000 years. The Grindelwald Fluctuation divides the Spörer Minimum from the Maunder Minimum.

That leads us to our second assumption: the idea that anthropogenic climate change began with industrialization. Most scholars of past climate change would still agree, but that might be changing. Recently, a growing body of evidence has started to suggest that humanity’s impact on Earth’s climate might be much older. Human depravity, it seems, might have been to blame for the cooling of the sixteenth century.Back in 2003, palaeoclimatologist William Ruddiman proposed that humans were to blame for preindustrial climate change, in a groundbreaking article that shocked the scientific community. Two years later, he thoroughly explained and defended his conclusions in book called Plows, Plagues, and Petroleum: How Humans Took Control of Climate. Ruddiman argued that humanity had slowly but progressively altered Earth’s atmosphere since the widespread adoption of agriculture. Some 8,000 years ago, communities in China, Europe, and India made room for agricultural monocultures by burning away forests. According to Ruddiman, the scale of deforestation was enough to steadily increase the concentration of atmospheric carbon dioxide. Then, from around 5,000 years ago, rice farming and, to a lesser extent, livestock cultivation slowly raised atmospheric methane concentrations. Ruddiman concluded that the cumulative effect of these anthropogenic greenhouse gas emissions was to gradually increase average global temperatures, and perhaps ward off another ice age.Ruddiman also argued that, since the adoption of agriculture, temporary fluctuations in atmospheric carbon dioxide concentrations followed from dramatic changes in human populations. During major disease outbreaks, Ruddiman insisted, populations declined to such an extent that agricultural land went untilled on a vast scale. Woodlands expanded, pulling more carbon dioxide out of the atmosphere than the agricultural crops they replaced, and thereby cooling the planet. When populations recovered, farmers burned down forests and planted their monocultures, warming the Earth. ​

Mesoamerican infected with smallpox, from the Florentine Codex by Bernardino de Sahagún.

​During the sixteenth century, Spanish soldiers and settlers established a vast empire by waging environmentally destructive wars on the indigenous peoples of central and southern America. They forced many of the survivors into new settlement patterns and gruelling forced labour. They also disrupted indigenous ways of life by appropriating, and often transforming, regional environments. Their animals, plants, and pathogens encountered virgin populations and spread rapidly. Indigenous communities in hot, humid climates were especially vulnerable to outbreaks of Eurasian crowd diseases, which included smallpox, measles, influenza, mumps, diphtheria, typhus, and pulmonary plague. Recent population modelling suggests that the population of the Americas declined from approximately 61 million in 1492 to six million in 1650.

By the late sixteenth century, this holocaust was well underway. Land previously colonized by indigenous communities through controlled burning or the planting of agricultural monocultures gradually reverted to woodlands. While all plants inhale carbon dioxide and exhale oxygen, tropical rainforests are much more effective carbon sinks than human crops. In the Americas, reforestation on a vast scale probably lowered atmospheric concentrations of carbon dioxide by 7 to 10 parts per million between 1570 and 1620. Human cruelty may therefore have contributed to the climatic cooling also caused by volcanic eruptions and, maybe, a decline in solar radiation relative to modern or medieval norms.

A Spanish depiction of Tenochtitlan, the Aztec capitol, 1524.

A growing body of scholarship now provides evidence for these relationships. However, there are many questions that must be answered before we can confidently conclude that depopulation helped trigger the Grindelwald Fluctuation, let alone other episodes of climatic cooling. For instance: did the cooling effect of sixteenth-century reforestation in the Americas overwhelm the warming influence of contemporaneous deforestation in China and India? Were invasive species introduced by Europeans into the Americas incapable of preventing reforestation? Was the pace of depopulation, and in turn reforestation, really so fast and so universal that it could substantially reduce atmospheric carbon dioxide concentrations over the course of a few decades?

It will take a while to answer these questions, but some scholars are already drawing big conclusions. Earlier this year, geographers Simon Lewis and Mark Maslin argued that the cooling set in motion by the depopulation of the Americas could be considered the beginning of the “Anthropocene,” the proposed geological epoch dominated by human transformations of the world’s environment. Dating big changes in geological time is tricky business. The changes must be visible in the global stratigraphic record – that is, in rock layers – and they must be traceable to a specific date. Lewis and Maslin lean on earlier environmental histories of the “Columbian Exchange,” the European transfer of plants, animals, and pathogens between the New and Old Worlds. The impact was a global biotic homogenization that, according to Lewis and Maslin, should be visible in the stratigraphic record. That still leaves them without a specific date, however. They settle on 1610, because that was when atmospheric carbon dioxide levels reached a minimum caused, they say, by European depopulation of the Americas. ​

Warships, stuck in the ice during the Dutch Revolt.

​There may be one more wrinkle to this sad story. In a forthcoming book, I argue that the Dutch revolt against the Spanish empire was provoked, in part, by high food prices that followed from harvest failures during the chilly onset of the Grindelwald Fluctuation. Then, until the early seventeenth century, the Dutch rebellion benefitted from a chilly climate. Dutch fortifications routinely forced Spanish armies to stay in the field during the frigid winters of the Grindelwald Fluctuation. The effect on Spanish soldiers could be disastrous. It is possible, therefore, that Spanish conquests in one part of the world contributed to climate changes that benefitted a rebellion against Spanish rule in another.

If so, the Eighty Years’ War may provide one of the first examples of such a self-defeating climate history of violence. It was certainly not the last. Recently, interdisciplinary researchers have found similar connections at work in the Syrian civil war. In a poorly governed society already destabilized by migrants fleeing the American invasion of Iraq, a severe drought caused, in part, by anthropogenic warming created fertile conditions for rebellion. The countries now at war in Syria and Iraq include those most responsible for the climate change that helped set the conflict in motion. Studying the Grindelwald Fluctuation may provide deep context for these relationships, by rooting them in a long history of violence and environmental transformation. It may also show that both assumptions commonly held about climate change are wrong.